1. Do Now: Anatomy of Punnett Squares
What do the letters across the top and left side of the Punnett square represent?
What do the combinations of alleles inside the 4 boxes represent?

2. Polygenic Inheritance
Polygenic traits are traits that are caused by more than one gene. For example, in parakeets, there are two genes for feather color, resulting in four different possible feather colors (there are also more colors possible, but they are caused by different genes) There is one gene that codes for a yellow pigment (C for the dominant yellow allele and c for the recessive white allele). There is also a second gene that codes for a blue pigment (B for the dominant blue gene, and b for the recessive white gene). In these birds, having both blue and yellow pigments gives the feathers a green color.

3. Dihybrid Cross
A dihybrid cross is a 4x4 Punnett square that can be used to calculate the probability of offspring with traits causes by more than one gene (polygenic inheritance) OR we can use them to look at two totally different traits.

4. Dihybrid Cross Looking at One Trait Caused by Two Genes
Feather color in parakeets is polygenic. There is one gene that produces a yellow color, and one that produces a blue color. Different combinations of alleles lead to different feather colors. BB or Bb = blue bb = no color (white) CC or Cc = yellow cc = no color (white)

5. Dihybrid Cross Looking at Two Traits
In this dihybrid cross, we are studying two different traits in peas (seed smoothness and seed color). We can use the dihybrid cross to calculate the probability of offspring receiving different combinations of the traits. For the wrinkled/smooth trait, R is dominant for smooth seeds, and r is recessive for wrinkled. Y is dominant for yellow seeds, and y is recessive for green seeds.

6. Let’s make a dihybrid cross together
In this dihybrid cross, we will look at two different genes that code for two different traits: flower color and height in pea plants. For height, use T for the dominant allele (tall) and t for recessive allele (short). For flower color, use P for the dominant allele (purple) and p for the recessive allele (white). We will cross two plants that are heterozygous for both traits. First, lets figure out what the genotypes of the parents are: Next, let’s figure out what the possible gametes are for each parent: Now, complete the cross! What are the ratios of genotypes? What are the ratios of phenotypes?

7. Now, get out the Meiosis Lab you started on Friday
At the start of the timer, you will have two minutes go to your notebook and get out the Meiosis lab so we can go over the pre-lab questions 1 and 2. You must have these questions answered before the lab tomorrow. Hold on to this for now.

8. Using a Microscope
We will watch a short video on how to use a microscope. This will be a review for most of you. Before we watch it, let’s read the questions together (they are in your handout). Using a Microscope Now, let’s go over the answers.

9. Microscope Handouts
You have a microscope handout in your notes with the parts of the microscope on one side and blanks for you to fill in on the other side. Right now, label all the parts of the microscope on the side with blanks. You may work with a partner, but you may not change seats.

10. Quiz Corrections
If there is time in class after you finish the microscope handout, you may start quiz corrections. Your homework is to finish the quiz corrections. You may not re-take the quiz unless you have completed the corrections.